1. Field of the Invention
Embodiments of the invention generally relate to a method and apparatus for conditioning a polishing pad.
2. Description of the Related Art
Electrochemical Mechanical Processing (ECMP) is a technique used to remove conductive materials from a substrate surface by electrochemical dissolution while concurrently polishing the substrate with reduced mechanical abrasion as compared to conventional Chemical Mechanical Polishing (CMP) processes. ECMP systems may generally be adapted for deposition of conductive material on the substrate by reversing the polarity of the bias applied between the substrate and an electrode. Electrochemical dissolution is performed by applying a bias between a cathode and a substrate surface to remove conductive materials from the substrate surface into a surrounding electrolyte. The bias may be applied to the substrate surface by a conductive contact disposed on or through a polishing material upon which the substrate is processed. The polishing material may be, for example, a processing pad disposed on a platen. A mechanical component of the polishing process is performed by providing relative motion between the substrate and the polishing material that enhances the removal of the conductive material from the substrate.
The processing pad is an important aspect of the ECMP process. The processing pad must have the appropriate mechanical properties for substrate planarization while minimizing the generation of defects in the substrate during polishing. Such defects may be scratches in the substrate surface caused by raised areas of the pad or by polishing by-products disposed on the surface of the pad, such as abraded portions of the pad, agglomerations of abrasive particles from a polishing slurry, removed materials from the substrate, and the like. The processing pad generally deteriorates naturally during polishing due to wear and/or accumulation of polishing by-products on the pad surface. Thus, the pad surface must periodically be refreshed, or conditioned, to restore the performance of the pad. Conventionally, a diamond conditioning disk is used to work the top layer of the pad surface into a state that possesses desirable polishing results. However, conventional conditioning processes that aggressively interact with the pad may have an adverse affect on the pad lifetime. Additionally, aggressive conditioning processes may cause parts of the conditioning element to come free and be left on the pad after conditioning, which may lead to scratches and defect generation on the substrate surface. Some processing pads withstand aggressive conditioning relatively well. Other processing pads are much more sensitive to conditioning by abrasion due to their low thickness, fragility and/or material of composition. Aggressive conditioning of these pads may result in pad damage and/or may severely reduce the pad lifetime, adding to lost service time for pad replacement and increased cost of production.
Another factor affecting the usable life of processing pads is copper by-product contamination. During ECMP of copper layers, copper by-products will precipitate out of the electrolyte solution. This copper precipitate will then contaminate the polishing pad as well as other areas of the polishing tool, i.e., the polishing head, the platen, the conditioning head, and the like. This precipitate does not dissolve in de-ionized water (DI water) and makes operation, rinsing and maintenance of the polishing pad and tool difficult.
Therefore, there is a need for an improved method for conditioning processing pads.